This invention relates generally to toner image reproduction, and more particularly to a single pass duplexing method and apparatus for producing duplex toner images on a sheet in a single pass of the sheet in a toner image reproduction machine.
In a typical electrostatographic reproduction process machine, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. A portion of the charged photoconductive member is irradiated or exposed to a light image of an document being reproduced, thereby selectively dissipating charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the document. The latent electrostatic latent image recorded on the photoconductive member is then developed by bringing a developer material into contact therewith. Generally, the developer material comprises charged toner particles in a liquid, or adhering triboelectrically to dry charged carrier granules or other suitable toner supporting material. During such development, the charged toner particles are attracted to the latent image forming a toner image on the photoconductive member. The toner image is then transferred from the photoconductive member to a copy sheet, and then heated to permanently affix it to the copy sheet. The foregoing generally describes a typical monochrome, for example, black and white electrostatographic reproduction process machine.
Several methods representing variations from the monochrome or single color process are known for producing multicolor images. In general, to produce multicolor images, different color components of a composite color image are formed and then put together in registration to achieve the composite color image. One multicolor image production method, for example, involves a process utilizing a plurality of different color toner development units, a single photoreceptor, and a multiple image frames single pass approach in which the monochrome or single color process is repeated for three or four cycles. In each cycle a component latent image of a composite multicolor final color is formed, and a toner of a different color is used to develop the component latent image.
Each developed component image as such is then transferred to the copy sheet. The process is repeated, for example, for cyan, magenta, yellow and black toner particles, with each color toner component image being sequentially transferred to the copy sheet in superimposed registration with the toner image previously transferred thereto. In this way, several toner component images, as are in the composite image, are transferred sequentially to the copy sheet, and can then be heated and permanently fused to the sheet.
A second method for producing color copies involves what is referred to as the tandem method which utilizes a plurality of independent imaging units for forming and developing latent component images, and a moving image receiving member such as an intermediate transfer roller or belt. In this method, the toned or developed component images from the imaging units are transferred in superimposed registration with one another to the intermediate roller or belt, thereby forming the multicolor composite image on the belt or roller. The composite image then can be transferred in one step to a sheet of copy paper for subsequent fusing.
A third method for producing color copies involves a single frame, single pass Recharge, Expose, and Develop (REaD) process. The REaD process uses a single photoreceptor, a single image frame thereon, and four imaging units each including imagewise exposure means and a development station containing a different color toner of cyan, magenta, yellow or black.
A composite subtractive multicolor image can thus be produced in a single pass, and on the single frame by charging, exposing and developing, then recharging, exposing and developing again utilizing this Recharge, Expose, and Develop (REaD) process architecture. In this process, digital version of the original or document is created pixel by pixel at a computer workstation or by a scanner. When created by scanning, light reflected from the original or document is first converted into an electrical signal by a raster input scanner (RIS), subjected to image processing, then reconverted into a light, pixel by pixel, by a raster output scanner (ROS).
In either case, the ROS exposes the charged photoconductive surface to record a latent image thereon corresponding to the subtractive color of one of the colors of the appropriately colored toner particles at a first development station. The photoconductive surface with the developed image thereon is recharged and re-exposed to record a latent image thereon corresponding to the subtractive primary of another color of the original. This latent image is developed with appropriately colored toner. This process (REaD) is repeated until all the different color toner layers are deposited in superimposed registration with one another on the photoconductive surface. The multi-layered toner image is transferred from the photoconductive surface to a sheet of copy paper. Thereafter, the toner image is fused to the sheet of copy paper to form a color copy of the original. The REaD process can also be performed as a multiple pass process.
In each of the different types of toner image reproduction machines described above, it is often necessary to produce duplex images or images on both sides of a copy sheet. Conventionally, in order to accomplish such production of duplex copies, or simply such xe2x80x9cduplexingxe2x80x9d, the copy sheet somehow has to be inverted either on the fly, or with the use of a duplex intermediate holding tray.
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Other features of the present invention will become apparent from the following drawings and description.